1. Field of the Invention
The present invention relates to a method of forming a protective sheath on coupled wire conductors, and more specifically to a method of protecting and fixing a position at which two different wire conductors are connected to each other for configuring various wiring systems.
2. Description of the Prior Art
Conventionally, when two wires covered by an insulating cover material such as vinyl resin are fixedly coupled to each other, each insulating cover material is first removed from a predetermined coupling position of each wire to expose each conductor; the two exposed conductors are twisted together or arranged in parallel to each other; a conductive sleeve is fitted or pressure fitted thereto or the two conductors are soldered to connect the two wire conductors; and finally, the conductor exposure portion is protected by winding an insulating tape therearound.
In this prior-art taping method, however, there exist various drawbacks in that the insulation of the coupled conductors is not perfect; the shape of the coupled conductors is not uniform; and further the strength is not sufficiently reliable.
To overcome these problems involved in the taping method, a method of forming an insulating sheath on the coupled conductors by resin molding method has been proposed instead of the insulating tape winding. In this method, the conductor coupled portion and the adjacent insulating cover material are set to a molding die, and a resin such as vinyl chloride resin is injected into the molding die to seal the conductor coupled portion and simultaneously form a new insulating resin sheath in tight contact with the insulating cover material.
In this molding method, however, even if the wire insulating cover material and the newly formed insulating sheath are made of the same material as vinyl chloride, since these two are not perfectly melted and welded to each other due to the presence of temperature difference within the molding die, the boundary of these two materials is not perfectly fixed and therefore it is difficult to prevent moisture from reaching the boundary between the two.
To improve the above-mentioned molding method, a bonding agent is applied on the surface of the wire insulating cover material, before being set to the molding die, to increase the adhesive strength between the two. In this prior-art wire coupling method, however, since the procedure is complicated as follows: two wire conductors are exposed and coupled to each other; a bonding agent is applied to the exposed conductor coupled portion; and the two coupled wires are set to the molding die, there exist problems in that the number of steps is large; the workability is not excellent; the adhesive strength is not yet sufficient; and the resin insulating sheath is apt to be formed into an eccentric condition.